Answer:
The magnitude of the torque about the origin is 108 N-m.
Explanation:
Given that,
Mass of the stone, m = 2 kg
Length of the string, l = 0.5 m
Angular velocity of the stone, 
The circle is parallel to the xy plane and is centered on the z axis, 0.75 m from the origin, r = 0.75 m
Firstly it is required to find the centripetal force acting on the stone. It is given by :


F = 144 N
Now the magnitude of the torque about the origin is given by :



So, the magnitude of the torque about the origin is 108 N-m. Hence, this is the required solution.